Methods and compositions for enhancing herbicidal activity

ABSTRACT

There is provided a method for enhancing the control of monocotyledenous and dicotyledenous plant species comprising applying to said plant species a combination of optically active R-imidazolinone compounds. Also provided is a herbicidal composition comprising a combination of R-imidazolinone compounds.

This application claims the benefit of Provisional Application No. 60/063,915 filed Oct. 31, 1997.

BACKGROUND OF THE INVENTION

Imidazolinone compounds and their herbicidal use are described in U.S. Pat. No. 4,798,619. Combinations of racemic imidazolinone compounds and their synergistic herbicidal effect are described in U.S. Pat. No. 5,030,271. The R and S optical isomers of imidazolinone compounds and their relative individual herbicidal effect are described in The Imidazolinone Herbicides, CRC Press, Inc. (1991).

In view of the imidazolinone art, in general, one would expect the R isomer of an imidazolinone compound to have a herbicidal effect of approximately 1.5-1.8 times greater than that of the corresponding racemic imidazolinone compound. Therefore, to the extent the combination of R-imidazolinone compounds behave as the combination of racemic imidazolinone compounds, one would expect a combination of R-imidazolinone compounds to demonstrate about a 1.5-1.8 times greater herbicidal effect than the corresponding combination of racemic imidazolinone compounds.

SUMMARY OF THE INVENTION

It has now been found, that combinations of the optically active R isomers of imidazolinone compounds such as R-imazethapyr and R-imazapyr demonstrate a surprisingly enhanced herbicidal effect when compared to the herbicidal effect of the corresponding combination of racemic compounds, as well as when compared to the herbicidal effect of the individual optically active R-imidazolinone components.

The present invention provides a method for enhancing the control of undesirable monocotyledenous and dicoty-ledenous plant species which comprises applying to the foliage of said plants or to the soil or water in which the seeds, tubers or other propagating organs thereof are growing or to he grown an effective amount of a combination of the R isomer of an imidazolinone compound plus the R isomer of a second different imidazolinone compound such as a combination of R-imazethapyr plus R-imazapyr.

The present invention also provides a herbicidal composition which comprises an inert liquid or solid carrier and an effective amount of a combination of R-imidazolinone compounds, such as a combination of R-imazethapyr plus, R-imazapyr.

DETAILED DESCRIPTION OF THE INVENTION

A constant concern in crop production is how to efficiently control weed competition with responsible ecological practices. One effective tool currently available to agriculturalists is the imidazolinone family herbicides. These compounds offer a mode of action which targets an enzyme which is only present in plants. Therefore, they are non-harmful to all non-plant life such as humans, animals, birds, fish and the like. Further, imidazolinone herbicides are effective at relatively low application rates. However, since they have a broad spectrum of weed control, and therefore, a variety of application uses, a new means of lowering the use rates needed to control weeds and diminishing the environmental load of active ingredient is desirable.

Surprisingly, it has now been found that the application of a combination of the R-isomer of one imidazolinone, or the salt thereof, with the R-isomer of another different imidazolinone, or the salt thereof, provides enhanced control of undesirable monocotyledenous and dicotyledenous plant species. The combination of R-imidazolinone compounds, or their salts, may be applied to the foliage or the soil or water in which the seeds, tubers or other propagating organs of said plant species are growing or are to be grown, preferably to the foliage. Advantageously, combinations of R-imidazolinones such as R-imazethapyr plus R-imazapyr, or the salts thereof demonstrate increased maize selectivity, particularly imidazolinone resistant or imidazolinone tolerant maize selectivity.

As used in the specification and claims, the term R-imidazolinone designates the optical isomer of an imidazolinone Compound having the R configuration assigned to the asymmetric carbon in the imidazolinone ring which is substituted by a methyl and an isopropyl group, for example an imidazolinone compound having the structure of formula I ##STR1## wherein R is H, or a cation; and

Y and Z are each independently H, C₁ -C₄ alkyl optionally substituted with C₁ -C₄ alkoxy or Y and Z may be taken together to represent --CH═CH--CH═CH--.

Examples of R-imidazolinone compounds of formula I useful in the method and composition of the invention include R-imazapyr, R-imazethapyr, R-imazaquin, R-imazamox, R-imazapic, and the like or a salt thereof, preferably R-imazethapyr and R-imazapyr or a salt thereof.

A cation, as used in the specification and claims, designates a positively charged moiety such as an alkali metal, an alkaline earth metal, ammonium, organic ammonium, manganese, copper, iron, zinc, cobalt, lead, silver, nickel and the like. Preferable cations are alkali metals, alkaline earth metals, ammonium or organic ammonium. Organic ammonium designates a positively charged nitrogen atom having one to four organic groups attached, such as alkyl, aryl or heteroaryl. The organic group may be cyclic or acyclic and may incorporate the positively charged nitrogen atom within the ring or without the ring. Preferable organic groups are alkyl groups such as isopropyl.

It is especially surprising that combinations comprising R-imatzethapyr plus R-imazapyr (or their salts) in a ratio of about 3 parts R-imazethapyr to one part R-imazapyr demonstrate a 2×-3× increase in weed control when compared to the corresponding combination of racemic imazethapyr plus racemic imazapyr (or their salts).

Advantageously, the method of invention may be used to enhance weed control at varied sites such as industrial, agricultural, recreational, ornamental and the like. In the instance of agricultural weed control, the method of invention is suitable for use in the presence of crop plant species and particularly in the presence of imidazolinone resistant or tolerant crop species such as legumes (e.g. peanuts or soybeans), IMI-CORN™, IMI™ canola, IMI™ wheat, IMI™ cotton, IMI™ rice and the like, especially IMI-CORN™.

The effective amount of the combination of R-imidazolinone compounds will vary according to the prevailing conditions such as weather, plant species, weed pressure, growth stage, mode of application, cultivation practice and the like. Generally effective amounts of a combination of R-imidazolinone compounds such as R-imazethapyr plus R-imazapyr may be about 0.003 kg/ha-0.250 kg/ha of R-imazethapyr plus about 0.001 kg/ha-0.083 kg/ha of R-imazapyr, preferably about 0.025-0.100 kg/ha of R-imazethapyr plus about 0.008-0.035 kg/ha of R-imazapyr.

In actual agricultural practice, the combination of R-imidazolinone compounds such as R-imazethapyr plus R-imazapyr may be applied simultaneously as a tank-mix partner or a co-formulant or sequentially as a separate application, preferably as a tank-mix partner or co-formulant. Therefore, the present invention also provides a herbicidal composition comprising an inert liquid or solid carrier and an effective amount of a combination of an R-imidazolinone compound plus a second different R-imidazolinone compound such as R-imazethapyr plus R-imazapyr or the salts thereof. Preferably, the R-imazethapyr and R-imazapyr, or their salts, are present in a ratio of about three parts of R-imazethapyr to one part R-imazapyr. Compositions of the invention include soluble granules, aqueous concentrates, dispersible granules, wettable powders, and the like, preferably soluble granules, aqueous concentrates or dispersible granules.

The agriculturally acceptable carrier may be a solid or liquid. Suitable solid carriers may be any inert carrier commonly used such as natural and synthetic clays and silicates, natural and synthetic resins, solid fertilizers and the like. Typical examples of a solid carrier include diatomaceous earth, talc, attapulgite, vermiculite, kaolinite, mica, calcium sulphate, silicon oxide, coumarone resin, polyvinyl chloride, styrene and the like. Similarly, suitable liquid carriers include water, glycols, alcohols, ketones, ethers, aromatic or araliphatic hydrocarbons, petroleum fractions, and the like, or mixtures thereof. Preferred carriers are water soluble carriers.

For a more clear understanding of the invention, specific examples thereof are set forth below. These examples are merely illustrative and are not to be understood as limiting the scope and underlying principles of the invention in any way. Indeed, various modifications of the invention, in addition to those shown and described herein, will become apparent to those skilled in the art from the following examples and foregoing description. Such modifications are also intended to fall within the scope of the appended claims.

EXAMPLE 1 Evaluation of the Enhanced Herbicidal Effect of the Combination of ohe R-Isomers of Imazethapyr and Imazapyr as Measured by Weed Control

In this evaluation, plants are grown in standard greenhouse soil for 10-14 days until they are at the 2- to 4-leaf stage. Said plants are then sprayed with an aqueous solution of the test compounds which contains 0.25% of a non-ionic surfactant and 1% of a 28-0-0 liquid fertilizer. Each treatment is replicated 3 to 4 times. Approximately 3 weeks after treatment visual ratings are made using the rating scale shown below. The data are averaged and shown on Table I.

    ______________________________________                                         Test Compound       Source                                                     ______________________________________                                         Imazethapyr         PURSUIT ®AS.sup.1                                      Imazapyr            ARSENAL ®AS.sup.1                                      Imazethapyr & Imazapyr                                                                             LIGHTNING ® AS.sup.1                                   R-imazethapyr       technical material.sup.2                                   R-imazapyr          technical material.sup.2                                   ______________________________________                                          .sup.1 Manufactured by American Cyanamid Co.                                   .sup.2 Formulated as an aqueous concentrate as described in U.S.               4,816,060.                                                               

    ______________________________________                                         Rating Scale                                                                              % Control                                                           Rating     (As Compared To Check)                                              ______________________________________                                         9          100                                                                 8          91-99                                                               7          80-90                                                               6          65-79                                                               5          45-64                                                               4          30-44                                                               3          16-29                                                               2           6-15                                                               1          1-5                                                                 0          No Effect                                                           ______________________________________                                    

    ______________________________________                                         PLANT SPECIES                                                                  Bayer                                                                          Code       Scientific Name  Common Name                                        ______________________________________                                         CHEAL      Chenopodium album, L.                                                                           Lambsquarters                                      AMBEL      Ambrosia artemisiifolia, L.                                                                     Ragweed                                            SETVI      Setaria viridis, (L) Beauv                                                                      Green Foxtail                                      ABUTH      Abutilon theophrasti, Medic.                                                                    Velvetleaf                                         ______________________________________                                    

                  TABLE I                                                          ______________________________________                                         Rate           WEED CONTROL                                                    Compound                                                                               g/ha       CHEAL   AMBEL  SETVI ABUTH                                  ______________________________________                                         Imazethapyr                                                                            4.00       2.5     2.5    3.5   2.5                                            8.00       2.3     2.8    4.5   3.0                                            16.00      3.5     4.0    4.3   4.0                                            32.00      7.0     6.0    6.0   6.3                                            64.00      8.0     6.5    7.5   6.3                                            96.00      9.0     7.5    9.0   9.0                                            128.00     9.0     8.8    9.0   9.0                                    R-Imazetha-                                                                            2.68       2.3     3.8    4.8   4.8                                    pyr     5.36       3.8     3.5    4.5   4.8                                            10.72      4.0     3.0    5.5   4.8                                            21.44      6.8     4.8    6.5   6.8                                            42.88      7.0     6.5    7.5   7.0                                            64.30      9.0     8.8    9.0   9.0                                            85.76      9.0     9.0    9.0   9.0                                    Imazapyr                                                                               2.016      6.3     2.5    5.3   4.8                                            4.00       8.0     4.0    6.8   6.3                                            8.00       8.8     5.0    9.0   7.5                                            16.00      9.0     7.0    9.0   8.5                                            32.00      9.0     7.8    9.0   9.0                                            48.00      9.0     8.8    9.0   9.0                                            64.00      9.0     8.8    9.0   9.0                                    R-Imazapyr                                                                             1.34       7.3     1.5    6.0   4.3                                            2.68       7.8     4.5    7.5   5.8                                            5.36       8.3     5.0    8.0   7.3                                            10.72      9.0     6.3    9.0   8.0                                            21.44      9.0     7.5    9.0   9.0                                            32.16      9.0     9.0    9.0   9.0                                            42.88      9.0     8.5    9.0   9.0                                    Imazethapyr                                                                            3.02 + 1.0 4.3     2.5    3.0   4.5                                    plus    6.0 + 2.0  6.5     3.3    6.0   4.8                                    Imazapyr                                                                               12.0 + 4.0 7.5     5.5    7.3   6.8                                            24.0 + 8.0 8.5     6.8    8.8   7.5                                            48 + 16    8.8     7.5    9.0   8.8                                            72 + 24    9.0     8.3    9.0   9.0                                            96 + 32    9.0     9.0    9.0   9.0                                    R-Imazetha-                                                                            2.01 + 0.67                                                                               5.3     4.3    5.5   5.5                                    pyr plus                                                                               4.02 + 1.34                                                                               9.0     5.5    7.3   7.3                                    R-Imazapyr                                                                             8.04 + 2.68                                                                               8.8     6.3    8.8   7.5                                            16.08 + 5.36                                                                              9.0     7.3    9.0   9.0                                            32.16 + 10.72                                                                             9.0     8.0    9.0   9.0                                            48.24 + 16.08                                                                             9.0     8.8    9.0   9.0                                            64.32 + 21.44                                                                             9.0     9.0    9.0   9.0                                    ______________________________________                                    

EXAMPLE 2 Evaluation of the Enhanced Herbicidal Effect of the Combination of the R-Isomers of Imazethapyr and Imazapyr as Measured by Fresh Weight

In this evaluation, plants are grown in standard greenhouse soil for 10-14 days until they are at the 2- to 4-leaf stage. Said plants are then sprayed with an aqueous solution of the test compounds which contains 0.25% of a non-ionic surfactant and 1% of a 28-0-0 liquid fertilizer. Test compounds used and the source thereof are the same as that described in Example 1. Each treatment is replicated 3 to 4 times. Approximately 3 weeks after treatment the plants are cut at the surface of the soil and weighed. The weights are reported as % of untreated check. The data are used to determine the rate at which a 50% plant growth inhibition as compared to the untreated check is obtained in grams per hectare. This rate is reported as the I₅₀ value. The I₅₀ values are calculated using the method described by Seefeldt, Jensen and Fuerst, Weed Technology, Vol. 9, p. 218-227 (1995). The I₅₀ values for the racemic test compounds and their corresponding R-isomers are compared and the ratio of I₅₀ -racemic/I₅₀ -R-isomer is recorded. The test results are shown in Table I, wherein the % fresh weight data are averaged.

    ______________________________________                                         PLANT SPECIES                                                                  Bayer                                                                          Code       Scientific Name  Common Name                                        ______________________________________                                         IPOSS      Ipomoea spp.     Morningglory                                       AMBEL      Ambrosia artemisiifolia, L.                                                                     Ragweed                                            ______________________________________                                    

                                      TABLE II                                     __________________________________________________________________________     IMAZETHAPYR    R-IMAZETHAPYR  IMAZPAYR                                         Rate  % Fresh Wt.                                                                             Rate  % Fresh Wt.                                                                             Rate  % Fresh Wt.                                g/ha  IPOSS                                                                              AMBEL                                                                               g/ha  IPOSS                                                                              AMBEL                                                                               g/ha  IPOSS                                                                              AMBEL                                  __________________________________________________________________________      4.00 76  92   2.68  82  51   2.02  69  95                                      8.00 76  79   5.36  82  81   4.00  60  61                                      16.00                                                                               69  60   10.72 67  65   8.00  33  44                                      32.00                                                                               59  37   21.44 69  49   16.00 20  16                                      64.00                                                                               47  29   42.88 51  33   32.00 16  4                                       96.00                                                                               27  5    64.30 20  3    48.00 13  1                                      128.00                                                                               25  2    85.76 16  0    64.00 12  1                                      I.sub.50                                                                             35.0                                                                               22.0       32.2                                                                               17.9       3.21                                                                               6.16                                   (g/ha)                                                                         Ratio  Racemic/R                                                                          ##STR2##                                                                                      ##STR3##                                                                                      ##STR4##                              __________________________________________________________________________                    RACEMIC        R-ISOMER                                         R-IMAZAPYR     COMBINATION.sup.1                                                                             COMBINATION.sup.2                                Rate  % Fresh Wt.                                                                             Rate  % Fresh Wt.                                                                             Rate  % Fresh Wt.                                g/ha  IPOSS                                                                              AMBEL                                                                               g/ha  IPOSS                                                                              AMBEL                                                                               g/ha  IPOSS                                                                              AMBEL                                  __________________________________________________________________________                    3.0            2.01                                             1.34  76  111  1.0   69  103  0.67  70  84                                                    6.0            4.02                                             2.68  57  76   2.0   63  92   1.34  68  57                                                    12.0           8.04                                             5.36  33  56   4.0   64  53   2.68  45  36                                                    24.0           16.08                                            10.72 27  30   8.0   53  36   5.36  29  12                                                    48.0           32.16                                            21.44 17  7    16.0  37  21   10.72 20  6                                                     72.0           48.24                                            32.16 11  2    24.0  20  2    16.08 18  2                                                     96.0           64.32                                            42.88 13  4    32.0  18  0    21.44 18  3                                      Ig.sub.50                                                                            2.12                                                                               5.94       15.2                                                                               20.5       5.60                                                                               6.60                                   (g/ha)                                                                         Ratio  Racemic/R                                                                          ##STR5##                                                                                  ##STR6##                                                                                      ##STR7##                                  __________________________________________________________________________      .sup.                                                                         1 Imazethapyr plus imazapyr                                                     .sup.2 Rimazethapyr plus Rimazapyr                                       

EXAMPLE 3 Field Evaluation of the Enhanced Herbicidal Effect of the Combination of the R-Isomers of Imazethapyr and Imazapyr

In this evaluation, small field plots having an average size of 3M×25M are used. All treatments are applied using a backpack sprayer. Test applications are made 19 days after planting a variety of weed species and IMI™-tolerant maize crops. Commercially available formulations of the test compounds are used where available. All combination treatments are tank-mixed prior to application. All treatments contain 0.25% of a nonionic surfactant and 1.0% of a 28-0-0 liquid fertilizer. Approximately 8 weeks after treatment, the plants are evaluated visually and % weed control is recorded. The data obtained are shown in Table III. Three varieties of IMI™-tolerant maize were used in this evaluation. At 8 weeks after treatment, no injury, such as stunting or chlorosis, was observed for all 3 varieties of maize.

    ______________________________________                                         Test Compound      Source                                                      ______________________________________                                         Imazethapyr        PURSUIT ®240 AS.sup.1                                   Imazapyr              ARSENAL ®240 AS.sup.1                                R-imazethapyr      technical material.sup.2                                    R-imazapyr         technical material.sup.2                                    ______________________________________                                          .sup.1 Manufactured by American Cyanamid Co.                                   .sup.2 Formulated as an aqueous concentrate as described in U.S.               4,816,060.                                                               

    ______________________________________                                         PLANT SPECIES                                                                  Bayer                                                                          Code   Scientific Name     Common Name                                         ______________________________________                                         BIDPI  Bidens pilosa L.    Beggartick, Hairy                                   CASOC  Cassia occidentalis Coffee senna                                        HELAV  Helianthus annuus, L.                                                                              Sunflower                                           DEDTO  Desmodium tortuosum, (SW)DC.                                                                       Beggarweed, Florida                                 BOILF  Borreria latifolia, Schum.                                                                         Buttonweed, broadleaf                               IAQGR  Ipomoea grandifolia Morningglory                                        SETGE  Setaria geniculata (Lam.)P. Beauv.                                                                 Foxtail, knotroot                                   BRAPL  Brachiaria plantaginea (Link)Hitche.                                                               Alexandergrass                                      DIGHO  Digitaria horizontalis, Wiild.                                                                     Crabgrass                                           CCHEC  Cenchrus echinatus, L.                                                                             Sandbur, Southern                                   PANMA  Panicum maximum, Jacq.                                                                             Guineagrass                                         ______________________________________                                    

                                      TABLE III                                    __________________________________________________________________________                 RATE                                                               TREATMENT   g/ha  BIDPI                                                                              CASOC                                                                              HELAV                                                                              DEDTO                                                                              BOILF                                                                              IAQGR                                                                              SETGE                                                                              BRAPL                                                                              DIGHO                                                                              CCHEC                                                                              PANMA                __________________________________________________________________________     Imazethapyr + Imazapyr                                                                     12 + 4                                                                               10  20  10  0   20  10  10  5   30  10  10                               24 + 8                                                                               20  40  30  10  25  25  30  20  50  20  20                               48 + 16                                                                              70  60  70  40  50  50  60  40  75  70  70                               96 + 32                                                                              100 90  100 60  90  85  95  90  97  95  90                   R-Imazethapyr +                                                                              8 + 2.7                                                                            20  40  25  10  40  30  20  10  30  10  20                   R-Imazapyr   16 + 5.3                                                                            40  60  70  30  60  50  35  20  80  25  30                               24 + 8                                                                               90  75  80  50  70  70  90  90  90  90  70                                 32 + 10.7                                                                          100 80  90  70  80  90  90  95  97  95  90                                 64 + 21.3                                                                          100 95  100 90  95  100 100 100 100 100 100                  __________________________________________________________________________

EXAMPLE 4 Field Evaluation of the Enhanced Herbicidal Effect of the Combination of the R-Isomers of Imazethapyr and Imazapyr

In this evaluation, small field plots (10M×2M) in which imidazolinone resistant (IR) corn plants have been sown are used. All treatments are applied, using a CO₂ sprayer, approximately 3 weeks after planting and are replicated 3 times. Commercially available formulations of test compounds are used where available. All treatments contain 0.25% of a nonionic surfactant and 1% of a 28-0-0 liquid fertilizer. At 27 and 62 days after treatment (DAT) visual observation of % weed control and % stunting are recorded. The data obtained are shown in Table IV.

    ______________________________________                                         Test Compound       Source                                                     ______________________________________                                         Imazethapyr + Imazapyr                                                                             PURSUIT ® 240 AS.sup.1 +                                                   ARSENAL ® 240 AS.sup.1                                 R-imazethapyr + R-imazapyr                                                                         technical material.sup.2                                   ______________________________________                                          .sup.1 Manufactured by American Cyanamid Co.                                   .sup.2 Formulated as an aqueous concentrate as described in U.S.               4,816,060.                                                               

    ______________________________________                                         PLANT SPECIES                                                                  Bayer                                                                          Code   Scientific Name     Common Name                                         ______________________________________                                         ANVCR  Anoda cristada, (L) Schlecht.                                                                      Spurred anoda                                       DIGSA  Digitaria, Sanguinalis, (LL) Scop.                                                                 Crabgrass                                           ELEIN  Eleusine indica, (L) Gaertn.                                                                       Goosegrass                                          POROL  Portulaca oleracea, (L)                                                                            Purslane                                            SORHAP Sorghum halepense (L) Pers.                                                                        Johnsongrass, rhizome                               ______________________________________                                    

                                      TABLE IV                                     __________________________________________________________________________                        % WEED CONTROL              %                                                  ANVCR DIGSA ELEIN                                                                               POROL SORHAP                                                                              Stunting                                     RATE  (Days after Treatment)      IR Corn                         TREATMENT    g/ha  27 62 27 62 27                                                                               62 27 62 27 62                                                                               27                              __________________________________________________________________________     Imazethapyr + Imazapyr                                                                      12 + 4                                                                               63 100                                                                               30 50 0 0  30 100                                                                               57 50                                                                               0                                            24 + 8                                                                               92 100                                                                               78 70 37                                                                               0  65 100                                                                               83 60                                                                               0                                            48 + 16                                                                              100                                                                               100                                                                               97 88 82                                                                               50 87 100                                                                               97 75                                                                               13                                           60 + 20                                                                              100                                                                               100                                                                               88 85 37                                                                               70 100                                                                               100                                                                               93 90                                                                               2                                            96 + 32                                                                              99 100                                                                               100                                                                               98 93                                                                               95 99 100                                                                               100                                                                               95                                                                               22                              R-Imazethapyr + R-Imazapyr                                                                    8 + 2.7                                                                            77 100                                                                               53 60 0 0  68 100                                                                               57 50                                                                               7                                             16 + 5.3                                                                            85 100                                                                               88 50 37                                                                               0  88 100                                                                               88 80                                                                               15                                           24 + 8                                                                               98 100                                                                               97 95 63                                                                               50 99 100                                                                               99 95                                                                               8                                              32 + 10.7                                                                          100                                                                               100                                                                               99 100                                                                               90                                                                               90 99 100                                                                               98 95                                                                               13                                             64 + 21.3                                                                          100                                                                               100                                                                               100                                                                               100                                                                               91                                                                               98 100                                                                               100                                                                               100                                                                               98                                                                               13                              __________________________________________________________________________

EXAMPLE 5 Field Evaluation of the Enhanced Herbicidal Effect of the Combination of the R-Isomers of Imazethapyr and Imazapyr

Using essentially the same procedure described in Example 4 and varying the location of the trial, a field evaluation of the combination of R-imazethapyr plus R-imazapyr is performed. Visual weed control evaluations are recorded at 36 and 69 days after treatment. Visual evaluation of % stunting of the IR corn crop is recorded at 36 days after treatment. The data obtained are shown in Table V.

    ______________________________________                                         PLANT SPECIES                                                                  Bayer                                                                          Code    Scientific Name   Common Name                                          ______________________________________                                         DIGSA   Digitaria sanguinalis, (L.)Scop.                                                                 Crabgrass                                            SORHAP  Sorghum halepense (L.) Pers.                                                                     Johnsongrass, rhizome                                ______________________________________                                    

                  TABLE V                                                          ______________________________________                                                       % Weed Control                                                                               %                                                                DIGSA   SORHAP    Stunting                                              Rate     (Days After Treatment)                                                                         IR Corn                                        Compound g/ha       36     69   36   69   36                                   ______________________________________                                         Imazethapyr                                                                             12 + 4     60     53   0    40   0                                    plus     24 + 8     93     77   --   68   0                                    Imazapyr 48 + 16    92     87   65   70   10                                            60 + 20    99     92   93   70   3                                             96 + 32    98     95   93   88   3                                    R-Imazethapyr                                                                             8 + 2.7  68     47   83   83   0                                    plus       16 + 5.35                                                                               92     77   80   83   0                                    R-Imazapyr                                                                              24 + 8     68     91   90   78   7                                               32 + 10.7                                                                               99     99   95   95   7                                               64 + 21.3                                                                               100    100  100  100  2                                    ______________________________________                                    

EXAMPLE 6 Postemergence Evaluation of the Enhanced Herbicidal Effect of the Combination of the R-Isomers of Imidazolinone Compounds

In this evaluation, plants are grown in standard greenhouse soil for 10-14 days until they are at the 2- to 4-leaf stage. Said plants are then sprayed with aqueous test solutions prepared from formulated technical material containing 0.25% of a non-ionic surfactant. Each treatment is replicated 3 to 4 times. After spraying, the plants are placed on greenhouse benches and cared for in a manner commensurate with conventional greenhouse practice. Approximately 3 weeks after treatment the plants are visually evaluated for % weed control as compared to the untreated check. The data are averaged and shown in Table VI.

    ______________________________________                                         PLANT SPECIES                                                                  Bayer                                                                          Code   Scientific Name     Common Name                                         ______________________________________                                         AMBEL  Ambrosia artemisiifolia, L.                                                                        Ragweed, common                                     PANMI  Panicum miliaceum, L.                                                                              Millet, wild proso                                  CYPRO  Cyperus rotundus, L.                                                                               Nutsedge, purple                                    IPOHE  Ipomoea hederacea, (L)Jacq.                                                                        Morningglory, ivyleaf                               ABUTH  Autilon theophrasti, Medic.                                                                        Velvetleaf                                          DIGSA  Digitaria sanguinalis, (L)Scop                                                                     Crabgrass                                           ECHCG  Echinochloa Crus-Galli, (L) Beau                                                                   Barnyardgrass                                       CHEAL  Chenopodium album, L.                                                                              Lambsquarters                                       CASOB  Senna obtusifolia, (L.)                                                                            Sicklepod                                           ______________________________________                                    

                                      TABLE VI                                     __________________________________________________________________________     Postemergence Herbicidal Evaluation                                            __________________________________________________________________________                  RATE   % WEED CONTROL                                             TREATMENT    g/ha   AMBEL                                                                               PANMI                                                                              CYPRO                                                                              IPOHE                                                                              ABUTH                                                                               DIGSA                                                                              CASOB                            __________________________________________________________________________     Imazaquin + Imazapyr                                                                        1.5 + 0.5                                                                             3    0   3   3   3    8   --                                            3 + 1  8    8   0   9   5    8   --                                            6 + 2  24   20  3   19  18   10  --                                            12 + 4 45   13  5   33  43   23  --                                             8 + 24                                                                               76   40  30  50  80   63  --                                            16 + 48                                                                               84   69  45  80  95   94  --                                            32 + 96                                                                               95   95  64  89  100  100 --                               R-Imazaquin + R-Imazapyr                                                                    1.5 + 0.5                                                                             13   6   0   0   6    5   --                                            3 + 1  15   30  3   4   10   15  --                                            6 + 2  38   13  10  36  29   18  --                                            12 + 4 69   33  34  53  53   48  --                                             8 + 24                                                                               85   78  48  79  96   88  --                                            16 + 48                                                                               90   95  50  88  100  100 --                                            32 + 96                                                                               99   100 65  93  100  100 --                               Imazamox + Imazapyr                                                                         0.75 + 0.25                                                                           5    0   5   0   0    0   --                                            1.5 + 0.5                                                                             14   6   0   3   16   0   --                                            3 + 1  31   46  24  21  29   11  --                                            6 + 2  58   28  20  29  54   31  --                                            12 + 4 68   66  23  50  85   68  --                                            24 + 8 78   83  45  71  100  93  --                                            48 + 16                                                                               96   97  74  84  96   99  --                               R-Imazamox + R-Imazapyr                                                                     0.75 + 0.25                                                                           11   23  3   6   5    5   --                                            1.5 + 0.5                                                                             16   31  5   10  14   6   --                                            3 + 1  28   14  14  16  35   15  --                                            6 + 2  53   54  10  45  59   19  --                                            12 + 4 78   65  30  60  91   73  --                                            24 + 8 90   93  50  81  100  94  --                                            48 + 16                                                                               97   98  73  91  100  100 --                               Imazapic + Imazapyr                                                                          0.25 + 0.125                                                                         0    0   0   0   --   --  0                                              0.5 + 0.25                                                                           0    1   1   0   --   --  0                                               1 + 0.5                                                                             0    5   3   5   --   --  3                                             2 + 1  11   48  5   20  --   --  6                                             4 + 2  21   91  8   79  --   --  15                                            8 + 4  73   100 20  81  --   --  49                                            16 + 8 88   100 64  95  --   --  74                               R-Imazapic + R-Imazapyr                                                                      0.25 + 0.125                                                                         0    0   0   0   --   --  0                                              0.5 + 0.25                                                                           0    0   0   0   --   --  0                                               1 + 0.5                                                                             5    46  3   33  --   --  3                                             2 + 1  21   71  21  68  --   --  8                                             4 + 2  48   100 5   73  --   --  54                                            8 + 4  88   100 25  90  --   --  74                                            16 + 8 86   100 61  94  --   --  83                               Imazethapyr + Imazapic                                                                      0.75 + 0.25                                                                           0    0   0   0   0    0   --                                            1.5 + 0.5                                                                             15   5   0   5   3    13  --                                            3 + 1  19   18  5   19  13   14  --                                            6 + 2  40   28  28  28  18   35  --                                            12 + 4 60   46  30  38  55   68  --                                            24 + 8 66   58  45  65  86   91  --                                            48 + 16                                                                               90   93  75  80  98   98  --                               R-Imazethapyr + R-Imazapic                                                                  0.75 + 0.25                                                                           10   0   10  0   3    5   --                                            1.5 + 0.5                                                                             10   20  5   3   5    5   --                                            3 + 1  20   8   5   13  18   16  --                                            6 + 2  50   38  21  25  64   43  --                                            12 + 4 53   80  28  53  73   65  --                                            24 + 8 86   80  45  75  88   93  --                                            48 + 16                                                                               91   98  89  96  89   99  --                               Imazaquin + Imazethapyr                                                                     4 + 2  10   1   1   16  --   --  0                                             8 + 4  34   20  14  15  --   --  1                                             16 + 8 71   73  15  71  --   --  1                                             32 + 16                                                                               81   90  53  75  --   --  29                                            64 + 32                                                                               86   93  50  80  --   --  65                               R-Imazaquin + R-Imazethapyr                                                                 4 + 2  24   26  6   8   --   --  3                                             8 + 4  51   55  38  53  --   --  8                                             16 + 8 69   58  16  70  --   --  8                                             32 + 16                                                                               88   88  65  76  --   --  43                                            64 + 32                                                                               95   96  71  83  --   --  75                               Imazaquin + Imazamox                                                                        6 + 2  11   0   4   6   10   0   --                                            12 + 4 24   3   8   10  21   6   --                                            24 + 8 35   15  9   18  30   38  --                                            48 + 16                                                                               71   45  23  39  71   84  --                                            96 + 32                                                                               78   66  29  60  89   98  --                               R-Imazaquin + R-Imazamox                                                                    6 + 2  13   3   9   8   14   6   --                                            12 + 4 26   5   9   9   18   20  --                                            24 + 8 64   19  18  24  33   50  --                                            48 + 16                                                                               76   54  29  48  76   89  --                                            96 + 32                                                                               85   79  65  65  80   94  --                               __________________________________________________________________________                         % WEED CONTROL                                                          RATE        AM- A-                                                TREATMENT    g/ha   CHEAL                                                                               BEL BUTH                                                                               CASOB                                                                              ECHCG                                                                               IPOHE                                __________________________________________________________________________     Imazethapyr + Imazamox                                                                       0.5 + 0.25                                                                           5    3   14  0   19   5                                                   1 + 0.5                                                                             28   9   19  0   58   36                                                2 + 1  23   41  50  0   64   43                                                4 + 2  39   63  63  3   71   63                                                8 + 4  58   75  80  4   85   76                                                16 + 8 65   76  80  30  99   73                                                32 + 16                                                                               77   83  98  53  99   79                                   R-Imazethapyr + R-Imazamox                                                                   0.5 + 0.25                                                                           3    6   14  3   15   1                                                   1 + 0.5                                                                             31   41  18  0   59   40                                                2 + 1  33   56  56  3   69   46                                                4 + 2  48   71  70  4   79   66                                                8 + 4  64   75  80  11  94   78                                                16 + 8 61   75  79  34  100  75                                                32 + 16                                                                               82   85  98  61  97   83                                   __________________________________________________________________________

EXAMPLE 7 Preemergence Evaluation of the Enhanced Herbicidal Effect of the Combination of the R-Isomers of Imidazolinone Compounds

In this evaluation, plant seeds are sown in pots containing a Sassafras sandy loam soil. Test solutions prepared as described in Example 6 are applied to the soil by spray application. After spraying, the plants are placed on greenhouse benches and cared for in a manner commensurate with convention al greenhouse practice. Each treatment was replicated 3-4, times. Approximately 3 weeks after treatment, visual evaluations of % weed control as compared to the untreated check are recorded. The data are averaged and shown in Table VII.

    ______________________________________                                         PLANT SPECIES                                                                  Bayer                                                                          Code    Scientific Name   Common Name                                          ______________________________________                                         CYPRO   Cyperus rotundus, L.                                                                             Nutsedge, purple                                     PANMI   Panicum miliaceum, L.                                                                            Millet, wild proso                                   AMBEL   Ambrosia artemisiifolia, L.                                                                      Ragweed, common                                      DIGSA   Digitaria sanguinalis, (L)Scop                                                                   Crabgrass                                            ABUTH   Abutilon theophrasti, Medic.                                                                     Velvetleaf                                           IPOHE   Ipomoea hederacea, (L)Jacq.                                                                      Morningglory, ivyleaf                                CASOB   Senna obtusifolia, L. Irwin and                                                                  Sicklepod                                                    Barneby                                                                ______________________________________                                    

                                      TABLE VII                                    __________________________________________________________________________     Preemergence Herbicidal Evaluation                                                          RATE  % WEED CONTROL                                              TREATMENT    g/ha  CYPRO                                                                              PANMI                                                                              AMBEL                                                                               DIGSA                                                                              ABUTH                                                                               IPOHE                                                                              CASOB                             __________________________________________________________________________     Imazamox + Imazapyr                                                                         0.75 + 0.25                                                                          1   3   1    5   21   1   --                                             1.5 + 0.5                                                                            3   4   4    4   61   28  --                                             3 + 1 6   9   5    23  83   46  --                                             6 + 2 40  38  33   31  63   56  --                                             12 + 4                                                                               44  59  60   45  99   75  --                                             24 + 8                                                                               81  75  71   69  95   79  --                                             48 + 16                                                                              94  89  79   93  95   84  --                                R-Imazamox + R-Imazapyr                                                                     0.75 + 0.25                                                                          3   5   4    3   19   3   --                                             1.5 + 0.5                                                                            5   1   6    6   23   8   --                                             3 + 1 5   4   3    10  48   20  --                                             6 + 2 21  39  18   45  85   64  --                                             12 + 4                                                                               61  73  59   55  98   79  --                                             24 + 8                                                                               81  76  68   79  100  81  --                                             48 + 16                                                                              84  86  75   91  96   84  --                                Imazapic + Imazapyr                                                                           1 + 0.5                                                                            0   26  3    --  --   50  0                                              2 + 1 3   61  41   --  --   77  28                                             4 + 2 54  73  45   --  --   81  35                                             8 + 4 70  79  74   --  --   84  73                                             16 + 8                                                                               83  81  82   --  --   91  93                                             32 + 16                                                                              97  90  91   --  --   90  93                                R-Imazapic + R-Imazapyr                                                                       1 + 0.5                                                                            0   31  11   --  --   52  0                                              2 + 1 31  69  63   --  --   75  38                                             4 + 2 66  78  68   --  --   84  65                                             8 + 4 75  87  75   --  --   88  51                                             16 + 8                                                                               96  92  93   --  --   90  98                                             32 + 16                                                                              100 95  94   --  --   92  94                                Imazaquin + Imazapyr                                                                        1.5 + 0.5                                                                            0   1   4    1   16   3   --                                             3 + 1 5   9   9    15  38   18  --                                             6 + 2 29  15  11   16  49   41  --                                             12 + 4                                                                               40  21  46   48  73   54  --                                             24 + 8                                                                               78  36  68   48  88   73  --                                             48 + 16                                                                              74  63  75   71  99   81  --                                             96 + 32                                                                              100 76  84   84  99   83  --                                R-Imazaquin + R-Imazapyr                                                                    1.5 + 0.5                                                                            4   3   9    4   21   4   --                                             3 + 1 10  0   11   11  35   1   --                                             6 + 2 13  6   25   9   59   40  --                                             12 + 4                                                                               29  30  65   43  78   69  --                                             24 + 8                                                                               64  50  76   66  89   74  --                                             48 + 16                                                                              84  69  75   71  89   80  --                                             96 + 32                                                                              90  74  81   94  99   81  --                                Imazaquin + Imazapic                                                                        2.25 + 0.5                                                                           3   3   6    --  --   8   10                                             4.5 + 1                                                                              4   16  9    --  --   44  3                                              9 + 2 34  58  59   --  --   76  14                                             18 + 4                                                                               65  80  78   --  --   76  14                                             36 + 8                                                                               71  96  91   --  --   94  80                                R-Imazaquin + R-Imazapic                                                                    2.25 + 0.5                                                                           1   13  28   --  --   38  13                                             4.5 + 1                                                                              11  45  48   --  --   70  25                                             9 + 2 48  66  79   --  --   85  33                                             18 + 4                                                                               83  87  89   --  --   91  70                                             36 + 8                                                                               99  97  96   --  --   93  91                                Imazaquin + Imazamox                                                                        3 + 1 0   3   0    3   0    3   --                                             6 + 2 0   3   16   5   48   16  --                                             12 + 4                                                                               0   6   46   45  59   50  --                                             24 + 8                                                                               5   29  84   63  81   73  --                                             48 + 16                                                                              28  61  91   71  94   85  --                                             96 + 32                                                                              68  90  97   90  98   97  --                                R-Imazaquin + R-Imazamox                                                                    3 + 1 0   3   14   4   40   10  --                                             6 + 2 1   3   58   33  53   24  --                                             12 + 4                                                                               6   53  65   53  73   71  --                                             24 + 8                                                                               11  63  75   73  84   78  --                                             48 + 16                                                                              59  78  92   84  95   94  --                                             96 + 32                                                                              80  99  98   98  98   93  --                                Imazaquin + Imazethapyr                                                                     4 + 2 0   6   9    16  33   0   --                                             8 + 4 8   13  25   30  64   45  --                                             16 + 8                                                                               46  59  74   60  80   78  --                                             32 + 16                                                                              68  68  86   71  83   80  --                                             64 + 32                                                                              84  81  93   86  93   91  --                                R-Imazaquin + R-Imazethapyr                                                                 4 + 2 4   20  31   20  59   0   --                                             8 + 4 28  51  71   60  68   0   --                                             16 + 8                                                                               75  64  83   73  83   78  --                                             32 + 16                                                                              86  84  95   80  93   91  --                                             64 + 32                                                                              97  89  95   97  97   94  --                                Imazethapyr + Imazamox                                                                      2 + 1 0   5   0    8   45   6   --                                             4 + 2 14  34  8    20  63   44  --                                             8 + 4 35  53  25   58  84   71  --                                             16 + 8                                                                               63  76  70   74  94   89  --                                             32 + 16                                                                              85  85  84   90  97   94  --                                R-Imazethapyr + R-Imazamox                                                                  2 + 1 4   14  3    14  58   11  --                                             4 + 2 18  25  23   40  71   35  --                                             8 + 4 43  49  55   51  84   69  --                                             16 + 8                                                                               80  76  79   76  93   88  --                                             32 + 16                                                                              91  90  88   92  97   94  --                                __________________________________________________________________________

EXAMPLE 8 Evaluation of the Enhanced Herbicidal Effect of the Combination of the R-Isomers of Imidazolinone Compounds in Imidazolinone Tolerant (IT) Corn

Field trials are conducted at various locations across the United States. The experimental design of each trial is a modified randomized complete block with a minimum 3 replications per treatment. Plot size is 10 to 12 feet wide and 30 to 40 feet long.

Planting time of IT corn varies depending on weather conditions and geographic region but is generally in late April to mid-June. Site preparation is consistent with local cultural practices and generally consists of 1 to 2 passes with a disc or field cultivator. IT Corn is sown in 30 inch rows.

Herbicides are applied with a tractor mounted sprayer equipped with a 10 to 12 foot boom, 8002 or 8003 flat fan nozzle tips, and delivering 20 gallons per acre (gpa) diluent volume pressurized at 35 to 45 psi. Postemergence herbicide application timings are based on weed and crop growth, and are generally at 1 to 3 inch weeds, or 5 to 8 inch corn.

Weed control in IT Corn trials is visually evaluated approximately 28 DAT (Table VIII)and 56 DAT (Table IX) and expressed as percent weed control (0 to 100% basis).

The data is averaged and shown in Tables VIII and Table IX.

                                      TABLE VIII                                   __________________________________________________________________________           Rate   giant   pitted                                                                             ivyleaf                                                                            fall broadleaf                                                                           purple                                                                              Texas                                                                               vevlet                              lbs/A  ragweed                                                                            Eclipta                                                                            mgg mgg panicum                                                                             signalgr                                                                            nutsedge                                                                            panicum                                                                             leaf                          __________________________________________________________________________     imazapic/                                                                               0.021 + .0042                                                                      69  75   80  95  97   90   67  72    99                           imazapyr                                                                       R-imazapic/                                                                          .014 + .003                                                                               776 92  98  99   90   65   70   99                            R-imazapyr                                                                     imazapic/                                                                               .032 + .0064                                                                       88  93  93  97  99   85   68   73   99                            imazapyr                                                                       R-imazapic/                                                                           .021 + .0042                                                                         76  97  87  100 98   86   50   53   99                            R-imazapyr                                                                     imazapic/                                                                               .047 + .0094                                                                       89  97  96  97  100  95   75   80   99                            imazapyr                                                                       R-imazapic/                                                                           .032 + .0064                                                                         87  95  95  98  100  93   73   75   99                            R-imazapyr                                                                     imazapic/                                                                              .094 + .019                                                                             966 97  97  100  96   80   80   99                            imazapyr                                                                       R-imazapic/                                                                          .064 + .013                                                                               986 97  96  100  96   80   83   99                            R-imazapyr                                                                     imazapic                                                                             0.047  82  89  91  96  100  89   73   77   99                            R-imazapic                                                                           0.032  84  90  89  96  99   80   60   62   99                            __________________________________________________________________________           Rate   woolly                                                                              sickle                                                                            Johnson                                                                            redroot                                                                            carpet                                                                             cult.d                                                                              giant                                                                              common                                                                               common                               lbs/A  cupgrass                                                                            pod                                                                               grass                                                                              pigweed                                                                            weed                                                                               sunflower                                                                           foxtail                                                                            waterhemp                                                                            cocklebur                      __________________________________________________________________________     imazapic/                                                                                 0.021 + .0042                                                                     96  55 93  53  53  100  95  85    90                             imazapyr                                                                       R-imazapic/                                                                            .014 + .003                                                                             94                                                                              81 90  82  80   95  99  88    96                             R-imazapyr                                                                     imazapic/                                                                                 .032 + .0064                                                                        93                                                                               82 82  85  85  100  99  87    93                             imazapyr                                                                       R-imazapic/                                                                             .021 + .0042                                                                          96                                                                               79 87  85  83   90  99  95    98                             R-imazapyr                                                                     imazapic/                                                                                 .047 + .0094                                                                        97                                                                               91 97  83  83  100  99  93    97                             imazapyr                                                                       R-imazapic/                                                                             .032 + .0064                                                                          99                                                                               86 98  80  80  100  99  90    93                             R-imazapyr                                                                     imazapic/                                                                                .094 + .019                                                                            9699                                                                              97  92  92  100  99  93    93                             imazapyr                                                                       R-imazapic/                                                                            .064 + .013                                                                              9699                                                                              95  95  95  100  100 80    93                             R-imazapyr                                                                     imazapic                                                                                  0.047                                                                                 81 93  80  82  1007 98  87    95                             R-imazapic                                                                              0.032                                                                                   80 82  83  87  1007 99  83    90                             __________________________________________________________________________

                                      TABLE IX                                     __________________________________________________________________________               Rate  water                                                                             fall green                                                                              Palmer                                                                             redroot                                                                            cockle                                                                             comm                                                                               barnyard                                                                            hairy                                                                              giant                                                                             shatter                                                                            giant                        lbs/A hemp                                                                              panicum                                                                             foxtail                                                                            amar                                                                               pigweed                                                                            bur lambs                                                                              grass                                                                               nightsh                                                                            foxt                                                                              cane                                                                               rag                __________________________________________________________________________     imazethapyr/imazapyr                                                                     .021 + .007                                                                          39 50   72  86  93  79  96  93   98  49 55  82                 R-imazethapyr/                                                                           .014 + .005                                                                          55 82   93  93  97  79  93  92   98  55 95  78                 R-imazapyr                                                                     imazethapyr/imazapyr                                                                     .042 + .014                                                                          43 78   96  95  98  85  96  94   98  74 100 40                 R-imazethapyr/                                                                           .028 + .009                                                                          58 99   99  95  98  91  95  97   97  76 100 37                 R-imazapyr                                                                     imazethapyr/imazapyr                                                                     .084 + .028                                                                          47 99   100 95  97  83  98  97   100 88 100 77                 R-imazethapyr/                                                                           .056 + .018                                                                          69 100  100 93  97  93  98  98   100 91 100 74                 R-imazapyr                                                                     __________________________________________________________________________ 

What is claimed is:
 1. A method for enhancing the control of undesirable monocotyledenous and dicotyledenous plant species which comprises applying to the foliage of said plant species or to the soil or water in which the seeds, tubers or other propagating organs thereof are growing or are to be grown an effective amount of a combination of at least two compounds selected from the group consisting of R-imazapyr or a salt thereof, R-imazethapyr or a salt thereof, R-imazaguin or a salt thereof, R-imazamox or a salt thereof, and R-imazapic or a salt thereof.
 2. The method according to claim 1 wherein the combination of R-imazethapyr or R-imazapic or a salt thereof plus R-imazapyr or a salt thereof is applied to the foliage of said plant species.
 3. The method according to claim 2 wherein said plant species are growing in the presence of maize.
 4. The method according to claim 3 wherein the maize is imidazolinone tolerant or imidazolinone resistant maize.
 5. A method for enhancing the control of undesirable monocotyledenous and dicotyledenous plant species which comprises applying to the foliage of said plant species or to the soil or water in which the seeds, tubers or other propagating organs thereof are growing or are to be grown an effective amount of a combination of R-imazethapyr or a salt thereof plus R-imazapyr, or a salt thereof wherein said R-imazethapyr or a salt thereof and R-imazapyr or a salt thereof are present in a ratio of three parts of R-imazethapyr to one part of R-imazapyr.
 6. A method for enhancing the control of undesirable monocotyledenous and dicotyledenous plant species which comprises applying to the foliage of said plant species or to the soil or water in which the seeds, tubers or other propagating organs thereof are growing or are to be grown an effective amount of a combination of R-imazethapyr or a salt thereof plus R-imazapyr, or a salt thereof wherein the combination is applied at a rate of about 0.003 kg/ha-0.250 kg/ha of R-imazethapyr plus about 0.001 kg/ha-0.083 kg/ha of R-imazapyr.
 7. The method according to claim 6 wherein the combination is applied at a rate of about 0.025 kg/ha-0.100 kg/ha of R-imazethapyr plus about 0.008 kg/ha-0.035 kg/ha of R-imazapyr.
 8. A herbicidal composition which comprises an inert liquid or solid carrier and an effective amount of a combination of R-imazethapyr or R-imazapic plus-R-imazapyr, or the salts thereof.
 9. A herbicidal composition which comprises an inert liquid or solid carrier and an effective amount of a combination of R-imazethapyr or R-imazapic plus-R-imazapyr, or the salts thereof wherein the R-imazethapyr or a salt thereof and R-imazapyr or a salt thereof are present in a ratio of about three parts R-imazethapyr to one part R-imazapyr.
 10. The composition according to claim 8 wherein said carrier is water soluble. 